A display device such as a flat panel display or a projector is, for example, provided with optical elements, in front of and behind each pixel, having a lens function or a light scattering function owing to a fine concave-convex structure, in order to realize a highly bright image by transmitting more light. Further, in a micro-chemical analysis device or a chemical synthesis device which uses a MEMS (Micro Electro Mechanical System) or a fluid control system with the MEMS, a fine concave-convex structure is formed on a glass surface, and the glass and the fine structure are joined to manufacture a liquid flow path or various analysis reaction mechanisms. Thus, there is demanded an efficient method for forming a fine concave-convex structure on a glass surface in conformity with a purpose.
In order to manufacture a glass molded body having a fine pattern of a concave-convex shape on a surface thereof, there has been conventionally used a method of transferring a die for molding to form the fine pattern. This method is a method of transferring a fine pattern of a die surface to glass by pressing a planar molding die having the fine pattern of the concave-convex shape formed on the die surface thereof to the glass heated to a softening temperature (for example, see Patent Reference 1).
However, in this method, it is necessary that the glass and the molding die are heated to a high temperature enough to soften the glass, which requires a long time period for molding, leading to a problem that productivity is low and an operational cost is high. Besides, the molding die is required to be formed of a heat-resistant material excellent in durability at a high temperature, which leads to a problem that a cost of material constituting a molding apparatus becomes high. Further, in a cooling process after transferring, deformation may occur in the fine pattern having been transferred to the glass, resulting in difficulty in accurate transferring.
In order to solve the above problems and to mold glass without applying a large load, Patent Reference 2 suggests a following method. That is, there is suggested a method of heating a glass material and a planar molding die to a temperature T in a range of Tg−150° C.<T<Tg+100° C., in relation to a glass transition temperature Tg of the glass material, and while keeping the glass material and the planar molding die in contact, applying a direct-current voltage (preferably, 100 V or more and 2000 V or less) between the glass material and the molding die to generate electrostatic attraction force between a surface of the glass material and a surface of the molding die, to thereby perform pressure molding by the electrostatic attraction force.
However, in the method described in Patent Reference 2, though concave-convex structure of the fine pattern transferred to the glass have a difference in height of a certain degree, the difference in height is not sufficient yet. Further, in this method, since an area of a glass substrate to be subjected to a transfer processing is limited to be equal to or less than an area of a die surface of the molding die, a large-sized molding die is necessary in order to process a large-area glass substrate, which leads to a problem that an equipment cost is substantially increased.
Further, as a glass substrate for a cover glass of a liquid crystal display or the like, a glass substrate which does not deteriorate characteristics of various functional films is demanded. In other words, conventionally, in a case of a glass substrate for a cover glass of a display device such as a liquid crystal display, especially a glass substrate having a thin film of metal or oxide formed on a surface thereof, if alkali metal oxide is contained in the glass, alkali metal ions eluted on the surface of the glass are diffused in the thin film to deteriorate a film characteristic. Thus, alkali-free glass not containing an alkali metal ion practically is used. However, there is demanded a glass substrate which uses a normal glass substrate containing an alkali metal ion and is usable as the glass substrate for the cover glass of the liquid crystal display or the like similarly to the alkali-free glass substrate.